Insects and other pests cost farmers billions of dollars annually in crop losses and in the expense of keeping these pests under control. The losses caused by insect pests in agricultural production environments include decrease in crop yield, reduced crop quality, and increased harvesting costs.
The corn rootworm (a coleopteran insect pest) is a serious plant pest. Extensive damage occurs to the United States corn crop each year due to root feeding by larvae of corn rootworm (Diabrotica spp.). It has been estimated that approximately 9.3 million acres of U.S. corn are infested with corn rootworm species complex each year. The corn rootworm species complex includes the Western corn rootworm (Diabrotica virgifera virgifera), Northern corn rootworm (Diabrotica barberi), and Southern corn rootworm (Diabrotica undecimpunctata howardi).
The life cycle of each Diabrotica species is similar. The eggs of the corn rootworm are deposited in the soil. Newly hatched larvae (the first instar) remain in the ground and feed on the smaller branching corn roots. Later instars of Western and Northern corn rootworms invade the inner root tissues that transport water and mineral elements to the plants. In most instances, larvae migrate to feed on the newest root growth. Tunneling into roots by the larvae results in damage which can be observed as brown, elongated scars on the root surface, tunneling within the roots, or varying degrees of pruning. Plants with pruned roots usually dislodge after storms that are accompanied by heavy rains and high winds. The larvae of Southern corn rootworm feed on the roots in a similar manner as the Western and Northern corn rootworm larvae. Southern corn rootworm larvae may also feed on the growing point of the stalk while it is still near the soil line, which may cause the plant to wilt and die.
After feeding for about 3 weeks, the corn rootworm larvae leave the roots and pupate in the soil. The adult beetles emerge from the soil and may feed on corn pollen and many other types of pollen, as well as on corn silks. Feeding on green silks can reduce pollination level, resulting in poor grain set and poor yield. The Western corn rootworm adult also feeds upon corn leaves, which can slow plant growth and, on rare occasions, kill plants of some corn varieties.
The soil-dwelling larvae of these Diabrotica species feed on the root of the corn plant, causing lodging. Lodging eventually reduces corn yield and often results in death of the plant. By feeding on cornsilks, the adult beetles reduce pollination and, therefore, detrimentally effect the yield of corn per plant. In addition, adults and larvae of the genus Diabrotica attack cucurbit crops (cucumbers, melons, squash, etc.) and many vegetable and field crops in commercial production as well as those being grown in home gardens.
It has been estimated that the annual cost of insecticides to control corn rootworm and the annual crop losses caused by corn rootworm damage exceeds a total of $1 billion in the United States each year (Meycalf, R. L. [1986] in Methods for the Study of Pest Diabrotica, Drysan, J. L. and T. A. Miller [Eds.], Springer-Verlag, New York, N.Y., pp. vii-xv). Approximately $250 million worth of insecticides are applied annually to control corn rootworms in the United States. In the Midwest, $60 million and $40 million worth of insecticide were applied in Iowa and Nebraska, respectively, in 1990. Even with insecticide use, rootworms cause about $750 million worth of crop damage each year, making them the most serious corn insect pest in the Midwest.
Control of corn rootworm has been partially addressed by cultivation methods, such as crop rotation and the application of high nitrogen levels to stimulate the growth of an adventitious root system. However, chemical insecticides are relied upon most heavily to guarantee the desired level of control. Insecticides are either banded onto or incorporated into the soil. Economic demands on the utilization of farmland restrict the use of crop rotation. In addition, an emerging two-year diapause (or overwintering) trait of Northern corn rootworms is disrupting crop rotations in some areas.
The use of insecticides to control corn rootworm also has several drawbacks. Continual use of insecticides has allowed resistant insects to evolve. Situations such as extremely high populations of larvae, heavy rains, and improper calibration of insecticide application equipment can result in poor control. Insecticide use often raises environmental concerns such as contamination of soil and of both surface and underground water supplies. The public has also become concerned about the amount of residual chemicals which might be found on food. Working with insecticides may also pose hazards to the persons applying them. Therefore, synthetic chemical pesticides are being increasingly scrutinized, and correctly so, for their potential toxic environmental consequences. Examples of widely used synthetic chemical pesticides include the organochlorines, e.g., DDT, mirex, kepone, lindane, aldrin, chlordane, aldicarb, and dieldrin; the organophosphates, e.g., chlorpyrifos, parathion, malathion, and diazinon; and carbamates. Stringent new restrictions on the use of pesticides and the elimination of some effective pesticides from the market place could limit economical and effective options for controlling costly pests.
Because of the problems associated with the use of organic synthetic chemical pesticides, there exists a clear need to limit the use of these agents and a need to identify alternative control agents. The replacement of synthetic chemical pesticides, or combination of these agents with biological pesticides, could reduce the levels of toxic chemicals in the environment.
A biological pesticidal agent that is enjoying increasing popularity is the soil microbe Bacillus thuringiensis (B.t.). The soil microbe Bacillus thuringiensis (B.t.) is a Gram-positive, spore-forming bacterium. Most strains of B.t. do not exhibit pesticidal activity. Some B.t. strains produce, and can be characterized by, parasporal crystalline protein inclusions. These xe2x80x9cxcex4-endotoxins,xe2x80x9d which typically have specific pesticidal activity, are different from exotoxins, which have a non-specific host range. These inclusions often appear microscopically as distinctively shaped crystals. The proteins can be highly toxic to pests and specific in their toxic activity. Certain B.t. toxin genes have been isolated and sequenced. The cloning and expression of a B.t. crystal protein gene in Escherichia coli was described in the published literature more than 15 years ago (Schnepf, H. E., H. R. Whiteley [1981] Proc. Natl. Acad. Sci. USA 78:2893-2897). In addition, with the use of genetic engineering techniques, new approaches for delivering B.t. toxins to agricultural environments are under development, including the use of plants genetically engineered with B.t. toxin genes for insect resistance and the use of stabilized intact microbial cells as B.t. toxin delivery vehicles (Gaertner, F. H., L. Kim [1988] TIBTECH 6:S4-S7). Thus, isolated B.t. endotoxin genes are becoming commercially valuable.
Until the last fifteen years, commercial use of B.t. pesticides has been largely restricted to a narrow range of lepidopteran (caterpillar) pests. Preparations of the spores and crystals of B. thuringiensis subsp. kurstaki have been used for many years as commercial insecticides for lepidopteran pests. For example, B. thuringiensis var. kurstaki HD-1 produces a crystalline xcex4-endotoxin which is toxic to the larvae of a number of lepidopteran insects.
In recent years, however, investigators have discovered B.t. pesticides with specificities for a much broader range of pests. For example, other species of B.t., namely israelensis and morrisoni (a.k.a. tenebrionis, a.k.a. B.t. M-7), have been used commercially to control insects of the orders Diptera and Coleoptera, respectively (Gaertner, F. H. [1989] xe2x80x9cCellular Delivery Systems for Insecticidal Proteins: Living and Non-Living Microorganisms,xe2x80x9d in Controlled Delivery of Crop Protection Agents, R. M. Wilkins, ed., Taylor and Francis, New York and London, 1990, pp. 245-255.). See also Couch, T. L. (1980) xe2x80x9cMosquito Pathogenicity of Bacillus thuringiensis var. israelensis,xe2x80x9d Developments in Industrial Microbiology 22:61-76; and Beegle, C. C. (1978) xe2x80x9cUse of Entomogenous Bacteria in Agroecosystems,xe2x80x9d Developments in Industrial Microbiology 20:97-104. Krieg, A., A. M. Huger, G. A. Langenbruch, W. Schnetter (1983) Z. ang. Ent. 96:500-508 describe Bacillus thuringiensis var. tenebrionis, which is reportedly active against two beetles in the order Coleoptera. These are the Colorado potato beetle, Leptinotarsa decemlineata, and Agelastica alni. 
Recently, new subspecies of B.t. have been identified, and genes responsible for active xcex4-endotoxin proteins have been isolated (Hxc3x6fte, H., H. R. Whiteley [1989] Microbiological Reviews 52(2):242-255). Hxc3x6fte and Whiteley classified B.t. crystal protein genes into four major classes. The classes were CryI (Lepidoptera-specific), CryII (Lepidoptera- and Diptera-specific), CryIII (Coleoptera-specific), and CryIV (Diptera-specific). The discovery of strains specifically toxic to other pests has been reported (Feitelson, J. S., J. Payne, L. Kim [1992] Bio/Technology 10:271-275). CryV has been proposed to designate a class of toxin genes that are nematode-specific. Lambert et al. (Lambert, B., L. Buysse, C. Decock, S. Jansens, C. Piens, B. Saey, J. Seurinck, K. van Audenhove, J. Van Rie, A. Van Vliet, M. Peferoen [1996] Appl. Environ. Microbiol 62(1):80-86) and Shevelev et al. ([1993] FEBS Lett. 336:79-82) describe the characterization of Cry9 toxins active against lepidopterans. Published PCT applications WO 94/05771 and WO 94/24264 also describe B.t. isolates active against lepidopteran pests. Gleave et al. ([1991] JGM 138:55-62) and Smulevitch et al. ([1991] FEBS Lett. 293:25-26) also describe B.t. toxins. A number of other classes of B.t. genes have now been identified.
The 1989 nomenclature and classification scheme of H8fte and Whiteley for crystal proteins was based on both the deduced amino acid sequence and the host range of the toxin. That system was adapted to cover 14 different types of toxin genes which were divided into five major classes. The number of sequenced Bacillus thuringiensis crystal protein genes currently stands at more than fifty. A revised nomenclature scheme has been proposed which is based solely on amino acid identity (Crickmore et al. [1996] Society for Invertebrate Pathology, 29th Annual Meeting, IIIrd International Colloquium on Bacillus thuringiensis, University of Cordoba, Cordoba, Spain, Sep. 1-6, 1996, abstract). The mnemonic xe2x80x9ccryxe2x80x9d has been retained for all of the toxin genes except cytA and cytB, which remain a separate class. Roman numerals have been exchanged for Arabic numerals in the primary rank, and the parentheses in the tertiary rank have been removed. Many of the original names have been retained, with the noted exceptions, although a number have been reclassified. See also xe2x80x9cRevisions of the Nomenclature for the Bacillus thuringiensis Pesticidal Crystal Proteins,xe2x80x9d N. Crickmore, D. R. Zeigler, J. Feitelson, E. Schnepf, J. Van Rie, D. Lereclus, J. Baum, and D. H. Dean, Microbiology and Molecular Biology Reviews (1998) Vol. 62:807-813; and Crickmore, Zeigler, Feitelson, Schnepf, Van Rie, Lereclus, Baum, and Dean, xe2x80x9cBacillus thuringiensis toxin nomenclaturexe2x80x9d (1999) available on Dr. Neil Crickmore""s website of the University of Sussex at Brighton. That system uses the freely available software applications CLUSTAL W and PHYLIP. The NEIGHBOR application within the PHYLIP package uses an arithmetic averages (UPGMA) algorithm.
As a result of extensive research and investment of resources, other patents have issued for new B.t. isolates and new uses of B.t. isolates. See Feitelson et al., supra, for a review. However, the discovery of new B.t. isolates and new uses of known B.t. isolates remains an empirical, unpredictable art.
Favret and Yousten ([1985] J. Invert. Path. 45:195-203) tested the insecticidal activity of Bacillus laterosporus strains, but concluded that the low levels of toxicity demonstrated by those strains indicate that those strains were not potential candidates for biocontrol agents. Montaldi and Roth (172 J. Bac. 4; April 1990; pp.2168-2171) conducted electron microscopy examination parasporal bodies of Bacillus laterosporus sporangia. Bone et al. (U.S. Pat. No. 5,045,314) report that the spores of selected strains of B. laterosporus inhibit egg hatching and/or larval development of an animal-parasitic nematode. Aronson et al. (U.S. Pat. No. 5,055,293) describe a spore-forming Bacillus laterosporus designated P5 (ATCC 53694). Bacillus laterosporus NRS-590 is used therein as a negative control. Aronson et al. postulate that B.l. P5 can either invade very young corn rootworm larvae for immediate or later damage or that it blocks the receipt or response of the rootworm to the corn root signal that directs it to the roots. WO 94/21795 and WO 96/10083 describe toxins that are purportedly active against certain pests. WO 98/18932 describes many new classes of microbial toxins that are active against various types of insects. Various probes and primers are also disclosed therein. Orlova et al. (64 Appl. Env. Micro. 7, July 1998, pp.2723-2725) report that the crystalline inclusions of certain strains of Bacillus laterosporus might potentially be used as candidates for mosquito control.
Obstacles to the successful agricultural use of B.t. toxins include the development of resistance to B.t. toxins by insects. In addition, certain insects can be refractory to the effects of B.t. The latter includes insects such as boll weevil and black cutworm as well as adult insects of most species which heretofore have demonstrated no apparent significant sensitivity to B.t. xcex4-endotoxins. While resistance management strategies in B.t. transgene plant technology have become of great interest, there remains a great need for developing genes that can be successfully expressed at adequate levels in plants in a manner that will result in the effective control of various insects.
The subject invention concerns materials and methods useful in the control of non-mammalian pests and, particularly, plant pests. In one embodiment, the subject invention provides novel, pesticidal toxins and toxin-encoding genes that are obtainable from Bacillus laterosporus isolates. In a preferred embodiment, the target pests are corn rootworm pests. The toxins of the subject invention include heat-labile, soluble toxins which can be obtained from the supernatant of cultures of the subject Bacillus laterosporus strains. The toxins of the subject invention also include smaller, heat-labile toxins obtainable from these strains.
The subject invention further provides nucleotide sequences which encode the toxins of the subject invention. The nucleotide sequences of the subject invention encode toxins which are distinct from previously-described toxins. The nucleotide sequences of the subject invention can also be used in the identification and characterization of genes which encode pesticidal toxins.
In one embodiment of the subject invention, the subject Bacillus isolates can be cultivated under conditions resulting in high multiplication of the microbe. After treating the microbes to provide single-stranded genomic nucleic acid, the DNA is characterized using nucleotide sequences according to the subject invention. Characteristic fragments of toxin-encoding genes will be amplified by the procedure, thus identifying the presence of the toxin-encoding gene(s).
In a preferred embodiment, the subject invention concerns plants and plant cells transformed to produce at least one of the pesticidal toxins of the subject invention such that the transformed plant cells express pesticidal toxins in tissues consumed by target pests. In addition, mixtures and/or combinations of toxins can be used according to the subject invention.
Transformation of plants with the genetic constructs disclosed herein can be accomplished using techniques well known to those skilled in the art and would typically involve modification of the gene to optimize expression of the toxin in plants.
The subject invention concerns materials and methods useful in the control of non-mammalian pests and, particularly, plant pests. In one embodiment, the subject invention provides novel, pesticidal toxins and toxin-encoding genes that are obtainable from Bacillus laterosporus (B.l.) isolates. In a preferred embodiment, the target pests are corn rootworm pests. The toxins of the subject invention include heat-labile, soluble toxins which can be obtained from the supernatant of cultures of the subject Bacillus laterosporus strains. MIS- and WAR-type toxins obtainable from these strains are described in detail, below. The toxins of the subject invention also include smaller, heat-labile toxins obtainable from these strains.
The subject invention further provides nucleotide sequences which encode the toxins of the subject invention. Nucleotide sequences of the subject invention encode toxins which are distinct from previously-described toxins. Other nucleotide sequences of the subject invention can also be used in diagnostic and analytic procedures that are well known in the art. For example, the probes, primers, and partial sequences can be used for identifying and characterizing genes which encode pesticidal toxins.
In one embodiment of the subject invention, the subject Bacillus isolates can be cultivated under conditions resulting in high multiplication of the microbe. After treating the microbes to provide single-stranded genomic nucleic acid, the DNA is characterized using nucleotide sequences according to the subject invention. Characteristic fragments of toxin-encoding genes will be amplified by the procedure, thus identifying the presence of the toxin-encoding gene(s).
In a preferred embodiment, the subject invention concerns plant cells transformed to produce at least one of the pesticidal toxins of the subject invention such that the transformed plant cells express pesticidal toxins in tissues consumed by target pests. In addition, mixtures and/or combinations of toxins can be used according to the subject invention. In some preferred embodiments, a MIS toxin and a WAR toxin are used together.
Transformation of plants with the genetic constructs disclosed herein can be accomplished using techniques well known to those skilled in the art and would typically involve modification of the gene to optimize expression of the toxin in plants.
Isolates useful according to the subject invention will be deposited in the permanent collection of the Agricultural Research Service Patent Culture Collection (NRRL), Northern Regional Research Center, 1815 North University Street, Peoria, Ill. 61604, USA. The culture repository numbers are as follows:
Cultures which have been deposited for the purposes of this patent application were deposited under conditions that assure that access to the cultures is available during the pendency of this patent application to one determined by the Commissioner of Patents and Trademarks to be entitled thereto under 37 CFR 1.14 and 35 U.S.C. 122. The deposits will be available as required by foreign patent laws in countries wherein counterparts of the subject application, or its progeny, are filed. However, it should be understood that the availability of a deposit does not constitute a license to practice the subject invention in derogation of patent rights granted by governmental action.
Further, the subject culture deposits will be stored and made available to the public in accord with the provisions of the Budapest Treaty for the Deposit of Microorganisms, i.e., they will be stored with all the care necessary to keep them viable and uncontaminated for a period of at least five years after the most recent request for the furnishing of a sample of the deposit, and in any case, for a period of at least thirty (30) years after the date of deposit or for the enforceable life of any patent which may issue disclosing the culture(s). The depositor acknowledges the duty to replace the deposit(s) should the depository be unable to furnish a sample when requested, due to the condition of a deposit. All restrictions on the availability to the public of the subject culture deposits will be irrevocably removed upon the granting of a patent disclosing them.
Mutants of the isolates referred to herein can be made by procedures well known in the art. For example, an asporogenous mutant can be obtained through ethylmethane sulfonate (EMS) mutagenesis of an isolate. The mutants can be made using ultraviolet light and nitrosoguanidine by procedures well known in the art.
In one embodiment, the subject invention concerns materials and methods including nucleotide primers and probes for isolating, characterizing, and identifying Bacillus genes encoding protein toxins which are active against non-mammalian pests. The nucleotide sequences described herein can also be used to identify new pesticidal Bacillus isolates. The invention further concerns the genes, isolates, and toxins identified using the methods and materials disclosed herein.
The new toxins and polynucleotide sequences provided here are defined according to several parameters. One characteristic of the toxins described herein is pesticidal activity. In a specific embodiment, these toxins have activity against Western corn rootworm. The toxins and genes of the subject invention can be further defined by their amino acid and nucleotide sequences. The sequences of the molecules can be defined in terms of homology to certain exemplified sequences as well as in terms of the ability to hybridize with, or be amplified by, certain exemplified probes and primers.
In a preferred embodiment, the MIS-type of toxins of the subject invention have a molecular weight of about 70 to about 100 kDa and, most preferably, the toxins have a size of about 80 kDa. Typically, these toxins are soluble and can be obtained from the supernatant of Bacillus cultures as described herein. These toxins have toxicity against non-mammalian pests. In a preferred embodiment, these toxins have activity against Western corn rootworm. The MIS proteins are further useful due to their ability to form pores in cells. These proteins can be used with second entities including, for example, other proteins. When used with a second entity, the MIS protein will facilitate entry of the second agent into a target cell. In a preferred embodiment, the MIS protein interacts with MIS receptors in a target cell and causes pore formation in the target cell. The second entity may be a toxin or another molecule whose entry into the cell is desired.
The subject invention further concerns WAR-type of toxins having a size of about 30-50 kDa and, most typically, have a size of about 40 kDa. Typically, these toxins are soluble and can be obtained from the supernatant of Bacillus cultures as described herein.
The MIS- and WAR-type of toxins of the subject invention can be identified with primers described herein.
Another unique type of toxin has been identified as being produced by the Bacillus strains of the subject invention. These toxins are much smaller than the MIS- and WAR-type of toxins of the subject invention. These toxins, like the MIS- and WAR-type of toxins, are heat labile. However, these toxins are in the approximate size range of about 10 kDa to about 1 kDa. These toxins are also soluble and can be obtained from the supernatants of Bacillus cultures as described herein.
With the teachings provided herein, one skilled in the art could readily produce and use the various toxins and polynucleotide sequences described herein.
Genes and Toxins. As used herein, the terms xe2x80x9cwild-type toxinxe2x80x9d and xe2x80x9cwild-type genexe2x80x9d refer to the genes and toxins naturally produced by the subject isolates (MB438 and MB439). The genes and toxins of the subject invention include not only the full length, wild-type sequences but also fragments of these sequences, variants, mutants, and fusion proteins which retain the characteristic pesticidal activity of the toxins specifically exemplified herein. For example, U.S. Pat. No. 5,605,793 describes methods for generating additional molecular diversity by using DNA reassembly after random fragmentation. Moreover, internal deletions can be made to the genes and toxins specifically exemplified herein, so long as the modified toxins retain pesticidal activity. Chimeric genes and toxins, produced by combining portions from more than one Bacillus toxin or gene, may also be utilized according to the teachings of the subject invention. As used herein, the terms xe2x80x9cvariantsxe2x80x9d or xe2x80x9cvariationsxe2x80x9d of genes refer to nucleotide sequences which encode the same toxins or which encode equivalent toxins having pesticidal activity. As used herein, the term xe2x80x9cequivalent toxinsxe2x80x9d refers to toxins having the same or essentially the same biological activity against the target pests as the exemplified toxins.
It is apparent to a person skilled in this art that genes encoding active toxins can be identified and obtained through several means. The specific genes exemplified herein may be obtained from the isolates deposited at a culture depository as described above. These genes, or portions or variants thereof, may also be constructed synthetically, for example, by use of a gene synthesizer. Variations of genes may be readily constructed using standard techniques for making point mutations. Also, fragments of these genes can be made using commercially available exonucleases or endonucleases according to standard procedures. For example, enzymes such as Bal31 or site-directed mutagenesis can be used to systematically cut off nucleotides from the ends of these genes. Also, genes which encode active fragments may be obtained using a variety of restriction enzymes. Proteases may be used to directly obtain active fragments of these toxins.
Equivalent toxins and/or genes encoding these equivalent toxins can be derived from Bacillus isolates and/or DNA libraries using the teachings provided herein. There are a number of methods for obtaining the pesticidal toxins of the instant invention. For example, antibodies to the pesticidal toxins disclosed and claimed herein can be used to identify and isolate toxins from a mixture of proteins. Specifically, antibodies may be raised to the portions of the toxins which are most constant and most distinct from other Bacillus toxins. These antibodies can then be used to specifically identify equivalent toxins with the characteristic activity by immunoprecipitation, enzyme linked immunosorbent assay (ELISA), or Western blotting. Antibodies to the toxins disclosed herein, or to equivalent toxins, or fragments of these toxins, can readily be prepared using standard procedures in this art. The genes which encode these toxins can then be obtained from the microorganism.
Fragments and equivalents which retain the pesticidal activity of the exemplified toxins are within the scope of the subject invention. Also, because of the redundancy of the genetic code, a variety of different DNA sequences can encode the amino acid sequences disclosed herein. It is well within the skill of a person trained in the art to create these alternative DNA sequences encoding the same, or essentially the same, toxins. These variant DNA sequences are within the scope of the subject invention. As used herein, reference to xe2x80x9cessentially the samexe2x80x9d sequence refers to sequences which have amino acid substitutions, deletions, additions, or insertions which do not materially affect pesticidal activity. Fragments retaining pesticidal activity are also included in this definition.
A further method for identifying the toxins and genes of the subject invention is through the use of oligonucleotide probes. These probes are detectable nucleotide sequences. Probes provide a rapid method for identifying toxin-encoding genes of the subject invention. The nucleotide segments which are used as probes according to the invention can be synthesized using a DNA synthesizer and standard procedures.
Certain toxins of the subject invention have been specifically exemplified herein. Since these toxins are merely exemplary of the toxins of the subject invention, it should be readily apparent that the subject invention comprises variant or equivalent toxins (and nucleotide sequences coding for equivalent toxins) having the same or similar pesticidal activity of the exemplified toxin. Equivalent toxins will have amino acid homology with an exemplified toxin. This amino acid identity will typically be greater than 60%, preferably be greater than 75%, more preferably greater than 80%, more preferably greater than 90%, and can be greater than 95%. These identities are as determined using standard alignment techniques, preferably those used by Crickmore et al. as discussed in the Background section of the subject Specification. The amino acid homology will be highest in critical regions of the toxin which account for biological activity or are involved in the determination of three-dimensional configuration which ultimately is responsible for the biological activity. In this regard, certain amino acid substitutions are acceptable and can be expected if these substitutions are in regions which are not critical to activity or are conservative amino acid substitutions which do not affect the three-dimensional configuration of the molecule. For example, amino acids may be placed in the following classes: non-polar, uncharged polar, basic, and acidic. Conservative substitutions whereby an amino acid of one class is replaced with another amino acid of the same type fall within the scope of the subject invention so long as the substitution does not materially alter the biological activity of the compound. Listed below in Table 1 are examples of amino acids belonging to each class.
In some instances, non-conservative substitutions can also be made. The critical factor is that these substitutions must not significantly detract from the biological activity of the toxin.
As used herein, reference to xe2x80x9cisolatedxe2x80x9d polynucleotides and/or xe2x80x9cpurifiedxe2x80x9d toxins refers to these molecules when they are not associated with the other molecules with which they would be found in nature. Thus, reference to xe2x80x9cisolated and purifiedxe2x80x9d signifies the involvement of the xe2x80x9chand of manxe2x80x9d as described herein. Chimeric toxins and genes also involve the xe2x80x9chand of man.xe2x80x9d
Recombinant Hosts. The toxin-encoding genes of the subject invention can be introduced into a wide variety of microbial or plant hosts. Expression of the toxin gene results, directly or indirectly, in the production and maintenance of the pesticide. The transformation of plant hosts is preferred. Pests that feed on the recombinant plant which expresses the toxin will thereby contact the toxin. With suitable microbial hosts, e.g., Pseudomonas, the microbes can be applied to the situs of the pest, where they will proliferate and be ingested. With any of the various approaches, the result is control of the pest. Alternatively, the microbe hosting the toxin gene can be killed and treated under conditions that prolong the activity of the toxin and stabilize the cell. The treated cell, which retains the toxic activity, then can be applied to the environment of the target pest. The Bacillus toxin can also be applied by introducing a gene via a suitable vector into a microbial host and then applying the host to the environment in a living state
A wide variety of ways are available for introducing a Bacillus gene encoding a toxin into a host under conditions which allow for stable maintenance and expression of the gene. These methods are well known to those skilled in the art and are described, for example, in U.S. Pat. No. 5,135,867, which is incorporated herein by reference.
Synthetic genes which are functionally equivalent to the toxins of the subject invention can also be used to transform hosts. Methods for the production of synthetic genes can be found in, for example, U.S. Pat. No. 5,380,831. In preferred embodiments, the genes of the subject invention are optimized for expression in plants.
Treatment of Cells. As mentioned above, Bacillus or recombinant cells expressing a Bacillus toxin can be treated to prolong the toxin activity and stabilize the cell. The pesticide microcapsule that is formed comprises the Bacillus toxin within a cellular structure that has been stabilized and will protect the toxin when the microcapsule is applied to the environment of the target pest. Suitable host cells may include either prokaryotes or eukaryotes. As hosts, of particular interest will be the prokaryotes and the lower eukaryotes, such as fungi. The cell will usually be intact and be substantially in the proliferative form when treated, rather than in a spore form.
Treatment of the microbial cell, e.g., a microbe containing the Bacillus toxin gene, can be by chemical or physical means, or by a combination of chemical and/or physical means, so long as the technique does not deleteriously affect the properties of the toxin, nor diminish the cellular capability of protecting the toxin. Methods for treatment of microbial cells are disclosed in U.S. Pat. Nos. 4,695,455 and 4,695,462, which are incorporated herein by reference.
Methods and Formulations for Control of Pests. Control of pests using the toxins, and genes of the subject invention can be accomplished by a variety of methods known to those skilled in the art. These methods include, for example, the application of Bacillus isolates to the pests (or their location), the application of recombinant microbes to the pests (or their locations), and the transformation of plants with genes which encode the pesticidal toxins of the subject invention. Transformations can be made by those skilled in the art using standard techniques. Materials necessary for these transformations are disclosed herein or are otherwise readily available to the skilled artisan.
Formulated bait granules containing an attractant and the toxins of the Bacillus isolates, or recombinant microbes comprising the genes obtainable from the Bacillus isolates disclosed herein, can be applied to the soil. Formulated product can also be applied as a seed-coating or root treatment or total plant treatment at later stages of the crop cycle. Plant and soil treatments of Bacillus cells may be employed as wettable powders, granules or dusts, by mixing with various inert materials, such as inorganic minerals (phyllosilicates, carbonates, sulfates, phosphates, and the like) or botanical materials (powdered corncobs, rice hulls, walnut shells, and the like). The formulations may include spreader-sticker adjuvants, stabilizing agents, other pesticidal additives, or surfactants. Liquid formulations may be aqueous-based or non-aqueous and employed as foams, gels, suspensions, emulsifiable concentrates, or the like. The ingredients may include Theological agents, surfactants, emulsifiers, dispersants, or polymers.
As would be appreciated by a person skilled in the art, the pesticidal concentration will vary widely depending upon the nature of the particular formulation, particularly whether it is a concentrate or to be used directly. The pesticide will be present in at least 1% by weight and may be 100% by weight. The dry formulations will have from about 1-95% by weight of the pesticide while the liquid formulations will generally be from about 1-60% by weight of the solids in the liquid phase. The formulations that contain cells will generally have from about 102 to about 104 cells/mg. These formulations will be administered at about 50 mg (liquid or dry) to 1 kg or more per hectare.
The formulations can be applied to the environment of the pest, e.g., soil and foliage, by spraying, dusting, sprinkling, or the like.
Polynucleotide Probes. It is well known that DNA possesses a fundamental property called base complementarity. In nature, DNA ordinarily exists in the form of pairs of anti-parallel strands, the bases on each strand projecting from that strand toward the opposite strand. The base adenine (A) on one strand will always be opposed to the base thymine (T) on the other strand, and the base guanine (G) will be opposed to the base cytosine (C). The bases are held in apposition by their ability to hydrogen bond in this specific way. Though each individual bond is relatively weak, the net effect of many adjacent hydrogen bonded bases, together with base stacking effects, is a stable joining of the two complementary strands. These bonds can be broken by treatments such as high pH or high temperature, and these conditions result in the dissociation, or xe2x80x9cdenaturation,xe2x80x9d of the two strands. If the DNA is then placed in conditions which make hydrogen bonding of the bases thermodynamically favorable, the DNA strands will anneal, or xe2x80x9chybridize,xe2x80x9d and reform the original double stranded DNA. If carried out under appropriate conditions, this hybridization can be highly specific. That is, only strands with a high degree of base complementarity will be able to form stable double stranded structures. The relationship of the specificity of hybridization to reaction conditions is well known. Thus, hybridization may be used to test whether two pieces of DNA are complementary in their base sequences. It is this hybridization mechanism which facilitates the use of probes of the subject invention to readily detect and characterize DNA sequences of interest.
The probes may be RNA, DNA, or PNA (peptide nucleic acid). The probe will normally have at least about 10 bases, more usually at least about 17 bases, and may have up to about 100 bases or more. Longer probes can readily be utilized, and such probes can be, for example, several kilobases in length. The probe sequence is designed to be at least substantially complementary to a portion of a gene encoding a toxin of interest. The probe need not have perfect complementarity to the sequence to which it hybridizes. The probes may be labeled utilizing techniques which are well known to those skilled in this art.
One approach for the use of the subject invention as probes entails first identifying by Southern blot analysis of a gene bank of the Bacillus isolate all DNA segments homologous with the disclosed nucleotide sequences. Thus, it is possible, without the aid of biological analysis, to know in advance the probable activity of many new Bacillus isolates, and of the individual gene products expressed by a given Bacillus isolate. Such a probe analysis provides a rapid method for identifying potentially commercially valuable insecticidal toxin genes within the multifarious subspecies of Bacillus.
One hybridization procedure useful according to the subject invention typically includes the initial steps of isolating the DNA sample of interest and purifying it chemically. Either lysed bacteria or total fractionated nucleic acid isolated from bacteria can be used. Cells can be treated using known techniques to liberate their DNA (and/or RNA). The DNA sample can be cut into pieces with an appropriate restriction enzyme. The pieces can be separated by size through electrophoresis in a gel, usually agarose or acrylamide. The pieces of interest can be transferred to an immobilizing membrane.
The particular hybridization technique is not essential to the subject invention. As improvements are made in hybridization techniques, they can be readily applied.
The probe and sample can then be combined in a hybridization buffer solution and held at an appropriate temperature until annealing occurs. Thereafter, the membrane is washed free of extraneous materials, leaving the sample and bound probe molecules typically detected and quantified by autoradiography and/or liquid scintillation counting. As is well known in the art, if the probe molecule and nucleic acid sample hybridize by forming a strong non-covalent bond between the two molecules, it can be reasonably assumed that the probe and sample are essentially identical. The probe""s detectable label provides a means for determining in a known manner whether hybridization has occurred.
In the use of the nucleotide segments as probes, the particular probe is labeled with any suitable label known to those skilled in the art, including radioactive and non-radioactive labels. Typical radioactive labels include 32P, 35S, or the like. Non-radioactive labels include, for example, ligands such as biotin or thyroxine, as well as enzymes such as hydrolases or perixodases, or the various chemiluminescers such as luciferin, or fluorescent compounds like fluorescein and its derivatives. The probes may be made inherently fluorescent as described in International Application No. WO 93/16094.
Various degrees of stringency of hybridization can be employed. The more stringent the conditions, the greater the complementarity that is required for duplex formation. Stringency can be controlled by temperature, probe concentration, probe length, ionic strength, time, and the like. Preferably, hybridization is conducted under moderate to high stringency conditions by techniques well known in the art, as described, for example, in Keller, G. H., M. M. Manak (1987) DNA Probes, Stockton Press, New York, N.Y., pp. 169-170. This information is hereby incorporated by reference.
As used herein xe2x80x9cmoderate to high stringencyxe2x80x9d conditions for hybridization refers to conditions which achieve the same, or about the same, degree of specificity of hybridization as the conditions employed by the current applicants. Examples of moderate and high stringency conditions are provided herein. Specifically, hybridization of immobilized DNA on Southern blots with 32P-labeled gene-specific probes was performed by standard methods (Maniatis et al.). In general, hybridization and subsequent washes were carried out under moderate to high stringency conditions that allowed for detection of target sequences with homology to the exemplified toxin genes. For double-stranded DNA gene probes, hybridization was carried out overnight at 20-25xc2x0 C. below the melting temperature (Tm) of the DNA hybrid in 6xc3x97SSPE, 5xc3x97Denhardt""s solution, 0.1% SDS, 0.1 mg/ml denatured DNA. The melting temperature is described by the following formula (Beltz, G. A., K. A. Jacobs, T. H. Eickbush, P. T. Cherbas, and F. C. Kafatos [1983] Methods of Enzymology, R. Wu, L. Grossman and K. Moldave [eds.] Academic Press, New York 100:266-285).
Tm=81.5xc2x0 C.+16.6Log[Na+]+0.41(%G+C)xe2x88x920.61(%formamide)xe2x88x92600/length of duplex in base pairs.
Washes are typically carried out as follows:
(1) Twice at room temperature for 15 minutes in 1xc3x97SSPE, 0.1% SDS (low stringency wash).
(2) Once at Tm-20xc2x0 C. for 15 minutes in 0.2xc3x97SSPE, 0.1% SDS (moderate stringency wash).
For oligonucleotide probes, hybridization was carried out overnight at 10-20xc2x0 C. below the melting temperature (Tm) of the hybrid in 6xc3x97SSPE, 5xc3x97Denhardt""s solution, 0.1% SDS, 0.1 mg/ml denatured DNA. Tm for oligonucleotide probes was determined by the following formula:
Tm(xc2x0 C.)=2(number T/A base pairs)+4(number G/C base pairs)
(Suggs, S. V., T. Miyake, E. H. Kawashime, M. J. Johnson, K. Itakura, and R. B. Wallace [1981] ICN-UCLA Symp. Dev. Biol. Using Purified Genes, D. D. Brown [ed.], Academic Press, New York, 23:683-693).
Washes were typically carried out as follows:
(1) Twice at room temperature for 15 minutes 1xc3x97SSPE, 0.1% SDS (low stringency wash).
(2) Once at the hybridization temperature for 15 minutes in 1xc3x97SSPE, 0.1% SDS (moderate stringency wash).
In general, salt and/or temperature can be altered to change stringency. With a labeled DNA fragment  greater than 70 or so bases in length, the following conditions can be used:
Duplex formation and stability depend on substantial complementarity between the two strands of a hybrid, and, as noted above, a certain degree of mismatch can be tolerated. Therefore, the probe sequences of the subject invention include mutations (both single and multiple), deletions, insertions of the described sequences, and combinations thereof, wherein said mutations, insertions and deletions permit formation of stable hybrids with the target polynucleotide of interest. Mutations, insertions, and deletions can be produced in a given polynucleotide sequence in many ways, and these methods are known to an ordinarily skilled artisan. Other methods may become known in the future.
Thus, mutational, insertional, and deletional variants of the disclosed nucleotide sequences can be readily prepared by methods which are well known to those skilled in the art. These variants can be used in the same manner as the exemplified primer sequences so long as the variants have substantial sequence homology with the original sequence. As used herein, substantial sequence homology refers to homology which is sufficient to enable the variant probe to function in the same capacity as the original probe. Preferably, this homology is greater than 50%; more preferably, this homology is greater than 75%; and most preferably, this homology is greater than 90%. The degree of homology or identity needed for the variant to function in its intended capacity will depend upon the intended use of the sequence. It is well within the skill of a person trained in this art to make mutational, insertional, and deletional mutations which are designed to improve the function of the sequence or otherwise provide a methodological advantage.
PCR Technology. Polymerase Chain Reaction (PCR) is a repetitive, enzymatic, primed synthesis of a nucleic acid sequence. This procedure is well known and commonly used by those skilled in this art (see Mullis, U.S. Pat. Nos. 4,683,195, 4,683,202, and 4,800,159; Saiki, Randall K., Stephen Scharf, Fred Faloona, Kary B. Mullis, Glenn T. Horn, Henry A. Erlich, Norman Ambeim [1985] xe2x80x9cEnzymatic Amplification of xcex2-Globin Genomic Sequences and Restriction Site Analysis for Diagnosis of Sickle Cell Anemia,xe2x80x9d Science 230:1350-1354.). PCR is based on the enzymatic amplification of a DNA fragment of interest that is flanked by two oligonucleotide primers that hybridize to opposite strands of the target sequence. The primers are oriented with the 3xe2x80x2 ends pointing towards each other. Repeated cycles of heat denaturation of the template, annealing of the primers to their complementary sequences, and extension of the annealed primers with a DNA polymerase result in the amplification of the segment defined by the 5xe2x80x2 ends of the PCR primers. Since the extension product of each primer can serve as a template for the other primer, each cycle essentially doubles the amount of DNA fragment produced in the previous cycle. This results in the exponential accumulation of the specific target fragment, up to several million-fold in a few hours. By using a thermostable DNA polymerase such as Taq polymerase, which is isolated from the thermophilic bacterium Thermus aquaticus, the amplification process can be completely automated. Other enzymes which can be used are known to those skilled in the art.
The DNA sequences of the subject invention can be used as primers for PCR amplification. In performing PCR amplification, a certain degree of mismatch can be tolerated between primer and template. Therefore, mutations, deletions, and insertions (especially additions of nucleotides to the 5xe2x80x2 end) of the exemplified primers fall within the scope of the subject invention. Mutations, insertions and deletions can be produced in a given primer by methods known to an ordinarily skilled artisan.
All of the references cited herein are hereby incorporated by reference.
Following are examples which illustrate procedures for practicing the invention. These examples should not be construed as limiting. All percentages are by weight and all solvent mixture proportions are by volume unless otherwise noted.